I'm new to tile set maps. I am trying to add MapBox layers that I made in TileMill (and have sitting in my MapBox Hosting account) into Open Layers. I have successfully added a non-transparent layer. I have also successfully added a transparent layer, however, that layer does not keep its transparency in Open Layers. It seems to put a white background behind it, thereby hiding anything underneath it.

I've seen this example which I can get to work fine, but does not address transparency.

I've tried adding every transparency option I can think of in Open Layers, but no luck. I'm wondering if maybe that XYZ format doesn't support transparency, because the Open Layers Getting Started tutorial Ex. 5 shows a working example using the WMS format (which has a transparent: "true", parameter.